CN1427960A - Optical device - Google Patents

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CN1427960A
CN1427960A CN01808870A CN01808870A CN1427960A CN 1427960 A CN1427960 A CN 1427960A CN 01808870 A CN01808870 A CN 01808870A CN 01808870 A CN01808870 A CN 01808870A CN 1427960 A CN1427960 A CN 1427960A
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band gap
refractive index
quasicrystal
photon
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CN1268953C (en
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杰里米·J·包姆博格
马丁·D·B·查尔顿
玛丽亚·C·内蒂
格雷戈里·J·帕克
马耶德·E·祖罗布
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Nanogan Ltd
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BTG International Ltd
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    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B82NANOTECHNOLOGY
    • B82YSPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y20/00Nanooptics, e.g. quantum optics or photonic crystals
    • CCHEMISTRY; METALLURGY
    • C30CRYSTAL GROWTH
    • C30BSINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/60Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape characterised by shape
    • CCHEMISTRY; METALLURGY
    • C30CRYSTAL GROWTH
    • C30BSINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B33/00After-treatment of single crystals or homogeneous polycrystalline material with defined structure
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122Basic optical elements, e.g. light-guiding paths
    • G02B6/1225Basic optical elements, e.g. light-guiding paths comprising photonic band-gap structures or photonic lattices

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Optics & Photonics (AREA)
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  • Optical Integrated Circuits (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

In order to create an optical device with a photonic band gap extending in two dimensions and with very uniform properties in any direction and for any polarisation state, to within 1 %, air holes are etched within a substrate of low refractive index material such silicon oxynitride or silica glass. The ratio of air hole area to the remainder of the substrate is low, being less than 35 %. The air holes define a quasicrystal structure, having twelve fold symmetry, being based on a square-triangle system. In another development, an etched substrate with a regular crystal structure or quasicrystal structure exhibits a non-linear refractive index. Two adjacent areas in such a substrate have different lattice properties, or have defects in the lattices, to create a unidirectional transmission path (diode action). A further beam of light may be used to modulate the transmission path by reason of the non-linear refractive index.

Description

Optical device
Technical field
The present invention relates to optical device, be specifically related to show the optical device of photonic band gap structure.
Background technology
In we previous application WO98/53351, a kind of method by means of radiation propagation characteristic in the photon band gap control waveguide is described.Support the material of radiation propagation under certain wavelength can make this device by etching, for example, visible radiation.This radiation can be visible radiation or other forms of electromagnetic radiation, for example, and ultraviolet, infrared and THZ tera hertz sesame radiation.In this instructions, term " optical radiation " comprises this other forms of radiation.
U.S. Patent No. 5,784,400 disclose a kind of optical device that contains resonator cavity, and it comprises: show the planar periodic dielectric structure of photon band gap and cause defective in the periodic dielectric structure of electronics mould in the photon band gap.Photon band gap is realized the interior space constraint of the face of the electromagnetic radiation of generation in this structure.The radiation that produces in the defect sturcture can be by means of propagating in the waveguide that forms in the photon band gap zone.In another embodiment, defective can be used for controlling from the input waveguide emission through the radiation frequency characteristic of defect sturcture to output waveguide.Yet, U.S. Patent No. 5,784,400 devices of being advised are linear substantially on its transport property.
U.S. Patent No. 5,559,825 propose a kind of photon band edge diode that utilizes a plurality of first and second dielectric layers structures.Second dielectric layer utilizes a kind of like this material to make, and between the incident intensity of this material and the different paths nonlinear relationship is arranged.These dielectric layers are arranged to lamination to transmit the spatial light anisotropy to the radiation delivery of passing through wherein.Utilize this device, exigent degree of accuracy is to produce required transport property when making this dielectric layer.In addition, because this structure, these devices are not easy to be integrated in the circuit arrangement with other optical devices.
Summary of the invention
In first aspect, the invention provides a kind of method of showing photonic band gap structure that forms, this method comprises:
A kind of material that stretches along two-dimensional directional is provided, and in described material, be formed with the first area of first refractive index, the first area is separated by the second area of second refractive index or a plurality of second area, long-range order and the unordered quasicrystal of short-term are determined to show in these zones, and show that n weighs symmetry, wherein n is more than or equal to 2, thereby a photon band gap that stretches along described two-dimensional directional at least is provided.
In second aspect, the invention provides a kind of structure of showing photon band gap,
Wherein this structure comprises the material that stretches along two-dimensional directional, this material comprises: the first area of first refractive index, the first area is separated by the second area of second refractive index or a plurality of second area, for a kind of long-range order and unordered quasicrystal of short-term showed is provided, and show that n weighs symmetry, wherein n is more than or equal to 2, thereby sets up a photon band gap that stretches along described two-dimensional directional at least.
The plane of symmetry that quasicrystal has is many more, and the isotropy of this quasicrystal optical property is just many more.It is roughly even that optical property becomes on all directions, particularly the width of photon band gap and centre frequency.For 12 heavy symmetry, optical property and can be evenly in 1% evenly in 4%.In addition, photon band gap can stretch along the third dimension direction perpendicular to this two-dimensional directional.Photon band gap is uniform for all polarization states.
Various forms of quasicrystals can be arranged, and quasicrystal can be only shows on the one dimension direction and changes that in the case, it has low symmetry, and 2 is heavy or greater than 2 weights.For the quasicrystal that different geometric shapes are arranged on two-dimensional directional, this quasicrystal can be showed any symmetries that weigh greater than 6, for example, 10 weights (Penrose paves), 15 weights, or higher.In a preferred embodiment, quasicrystal is based on and has 12 heavy symmetric square at random-triangle tiled systems.This is to be suitable for carrying out easily the structure cell that photoetching is reproduced because this system has in material substrate.The structure of paving based on Penrose does not have the structure cell that can easily duplicate by photoetching.Another scheme is that structure cell is based on the Archimedes who knows and paves (tiling).
In the third aspect, the invention provides a kind of method of showing photonic band gap structure that forms, this method comprises:
A kind of material that stretches and have relative low-refraction along two-dimensional directional is provided, refractive index is less than or equal to 3, with the first area that in described layer, is formed with first refractive index, the first area is separated by the second area of second refractive index or a plurality of second area, long-range order and the unordered quasicrystal of short-term are determined to show in these zones, and show the heavy symmetry of n, wherein n is more than or equal to 2, thereby sets up a photon band gap that stretches along described two-dimensional directional at least.
The material of two-dimensional layer can be a silicon, germanium, and silicon nitride or silicon oxynitride, or any other semiconductor material commonly used in the photon application, for example, indium phosphide or arsenic potassium, or comprise these mixtures of material alloys, or plastics.Yet, low-index material preferably, for example, silicon nitride or silicon oxynitride, or amorphous material, for example, quartz, or plastics.Use the major advantage of low-refraction to be, when being subjected to little loss or retroreflection, coupling comes the light of self-waveguide or glass optical fiber or other low-index materials to enter this structure easily.In this instructions, we consider specific inductive capacity, specific inductive capacity equal refractive index square.
In fourth aspect, the invention provides a kind of method of showing photonic band gap structure that forms, this method comprises:
A kind of material that stretches along two-dimensional directional is provided, and in described material, be formed with the first area of first refractive index, the first area is separated by the second area of second refractive index or a plurality of second area, long-range order and the unordered quasicrystal of short-term are determined to show in these zones, and show that n weighs symmetry, n 〉=12 wherein, thus a photon band gap that stretches along described two-dimensional directional at least set up.
This material can stretch along three-dimensional, determines that quasi-crystalline zone can be along the 3rd direction stretching, extension perpendicular to this two-dimensional directional.In one embodiment, quasicrystal structures can form the covering or the fibre core of optical fiber, and these zones are determined along the quasicrystal of fiber length stretching, extension.In another embodiment, quasi-crystalline zone can form cubical array, in order that the quasicrystal geometric shape along three-dimensional is provided.In another embodiment, the first area form along one dimension direction wherein stretch rectangular, the space length between each is rectangular is non-linear, in order that this two-dimentional band gap is provided.In a preferred embodiment, the quasicrystal geometric shape is only determined on described two-dimensional directional.
Aspect the 5th, the invention provides a kind of method of showing photonic band gap structure that forms, this method comprises:
A kind of material that stretches along two-dimensional directional is provided, and this material of etching is to remove the material in the predetermined area, etching is to stretch along the direction perpendicular to described two-dimensional directional, thereby define the first area of first refractive index, the first area is separated by the second area of second refractive index or a plurality of second area, thereby determines to show long-range order and the unordered quasicrystal of short-term, and show that n weighs symmetry, wherein n is more than or equal to 2, thus set up one at least along the photon band gap of described two-dimensional directional and
Wherein the ratio of first area area and second area area is relatively low, and it is less than 35%.
Using the advantage of low ratio is that etching process is simplified, and can accurately determine and increase work efficiency.
In further research, we have developed and have showed photon band gap and the non-linear of electromagnetic radiation arranged, the device of controlled and/or asymmetrical transmission characteristic, and these devices can be used as switch, transistor or diode.
According to another aspect of the present invention, provide a kind of structure of showing photon band gap.
Wherein this structure comprises: the first area material that first refractive index is arranged, the first area is separated by the second area of second refractive index or a plurality of second area, in order that a kind of crystal or quasicrystal structures of showing photon band gap is provided, wherein the character of this structural change material is to bring out significant nonlinear effect, and wherein the refractive index of this structure depends on that light incides this structural power.
A surprising feature of the present invention is, changes according to the present invention not have remarkable nonlinear material, and for example, silicon nitride makes it have significant nonlinear effect.
According to another aspect of the present invention, a kind of optical device is provided, comprise: the entity that has a paths at least, the optical radiation transmission is by this path, wherein the time across described path, the transport property of described radiation is subjected to the constraint of interior first area of described entity and second area, and comprise: a kind of material or the multiple material of showing photon band gap, position between wherein said first area and second area are mutual is such, the relevant evanscent field of the described first area photon band gap evanscent field relevant with described second area photon band gap interacted, thereby making described transport property is non-linear basically, asymmetric or controlled.
According to another aspect of the present invention, a kind of optical device that has by the light transmission path of the first and second adjacent areas is provided, each area is to be made by a kind of like this material, the first area of first refractive index is separated by the second area of second refractive index or a plurality of second area, described zone defines the crystal or the quasicrystal structures of photon band gap, each this structure is defectiveness therein, thereby in band gap, set up photon state and relevant evanscent field, the evanscent field of first area and second area is coupled mutually, thereby allow to transmit in photon band gap, transport property is non-linear or asymmetrical.
By the arrangement photon state different slightly energy is arranged, thereby produce diode action, because the transmission of the transfer ratio of light from the high-energy state to the low-energy state from the low-energy state to the high-energy state is easier.In addition, nonlinear characteristic of the present invention provides a kind of mechanism that can absorb excess energy.
According to another aspect of the present invention, a kind of optical device that has by the light transmission path of the first and second adjacent areas is provided, each area is to be made by a kind of like this material along two-dimensional directional, this material comprises: the first area of first refractive index, the first area of first refractive index is separated by the second area of second refractive index or a plurality of second area, these zones define the crystal or the quasicrystal structures of photon band gap, photon band gap in these two areas has different values, preferably, at least one area is showed nonlinear refractive index in first area and the second area, therefore, incide light adjustment on this area with respect to the band gap magnitude of another area band gap.
According to a first aspect of the present invention, this structure can be showed 12 heavy symmetry; Perhaps, they can be formed by the triangle (sixfold) or square (4 weight) dot matrix of low symmetry.
Preferably, at least one area is the defectiveness position therein, with block lattice site relatively, defective bit is that position or the difformity by one group of big or slightly little slightly diameter or refractive index constitutes.Perhaps, defective can be to be formed by the lattice site of losing, or is positioned at non-lattice site and is formed by described first area.In crystal was set up the wavelength coverage of photon band gap, these defectives had the effect of introducing narrow defective mould.The wavelength of this defective mould depends on flaw size significantly.
Preferably, the size of defective is different from the size of defective in the second area in the first area, though the defective in each zone has identical size.Each defective is set up the microdischarge cavities that can support wavelength local mode in the photon band gap.Though defective mould localization is at defective locations, it has relative evanscent field function.Evanscent field in two zones is overlapping at boundary, and photon just can shift between these two zones.
In addition, according to the present invention, the defective mould in two zones can be set up the energy state of different-energy value and different wave length value.Therefore, light can be transferred to the low-energy state of adjacent area from the high-energy state in a zone, this energy difference in second area by absorptions such as lattice vibrations.Yet when light transmitted in opposite direction, light need obtain energy so that transmit in high-energy state, and common neither one can absorb the mechanism of excess energy.Therefore, light just is reflected, and it can not transmit along opposite direction.
Description of drawings
Specifically describe the present invention referring now to accompanying drawing and by means of example, wherein:
Fig. 1 to 14 is curve maps of the photonic band gap structure character of explanation used triangle dot matrix of the present invention and square dot matrix;
Figure 15 (a) (b) and (c) is the quasicrystal structures according to one embodiment of the invention;
Figure 16 to 32 is optical property curve maps of structure among explanation Figure 15;
Figure 33,35 and 36 is scanning electron miniature figure and photos relevant with quasicrystal structures;
Figure 37 to 45 is diagrammatic representations of one group of second embodiment of the present invention;
The experiment transmission spectrum of the triangle dot matrix of Figure 46 and 47 expression one aspect of the invention.
Embodiment
The desirable attributes of photonic crystal is that band gap should stretch along any direction in the three-dimensional, and should be present in all polarization states, that is, and and the combination in any of transverse electric (TE) attitude and horizontal magnetic (TM) attitude and these two kinds of attitudes.This is because if band gap is non-isotropic, the risk that then exists photon to leak along some direction.
We find that the two-dimensional periodic structure of limited thickness can have the band gap that stretches along three-dimensional, and band gap can be held open in polarizers of big angle scope.
By means of periodicity triangle and hexagonal-lattice structure, though can provide along the photon band gap of two and three dimensions direction, but this only may be realizing in the high dielectric constant materials very much, and when being coupled to optical fiber, it causes unnecessary retroreflection and loss.
We have found such structure, and this structure can provide isotropic band gap in the material of low-k.In addition, utilize in the base material etching clearance to make under the situation of this material, only require very little air coefficient of admission.This helps to reduce scattering loss.
With reference to Fig. 1-14, utilize the two dimensional surface wave analysis, determine the photon character of silicon based photon crystal.Edge by drawing absolute photon band gap and the relation between the air coefficient of admission can be constructed photon band gap air coefficient of admission (a.f.f.) figure.In these curve maps, the function of the frequency range of photon band gap as rod (rod) diameter or air coefficient of admission pointed out on the island that curve surrounds.These curve maps produce the useful quantitative information of relevant photon band gap performance as lattice geometry and specific inductive capacity function.Can estimate the squares and triangles array of etching air pore in the silicon and the air coefficient of admission figure of inverse structure (the squares and triangles array of silicon rod in the air).In order to obtain universality, this result is that the scaling figure with any wavelength (λ) and lattice distance (Λ) draws.
(the band gap coefficient of admission figure of Γ-J and Γ-X), the most extreme variation in the expection band structure, and these curves are superposeed can keep the directed information of relevant band gap performance to estimate two main symmetry directions respectively.The frequency range of complete (non-directional) photon band gap is pointed out in the overlapping region on two groups of band gap island.Non-overlapping Domain is pointed out branch (orientation) photon band gap.Though estimate the band structure of two extreme polarization states (TE and TM) in each case, these data can be used for predicting the photonic crystal properties under any other linear polarization state.
When linearly polarized light incided on the photonic crystal, if wave vector is rotated slightly with respect to net plane, then E wave vector and H wave vector had the component that decomposes in this net plane simultaneously.So photon character is represented the feature of TE wavestrip and TM wavestrip structure.This characteristic strength is proportional in the net plane relative amplitude of wave vector separately.
Air coefficient of admission (fraction) on a large scale in, for TE and TM polarization state, separate analysis is etched in the silicon (n=3.46) two-dimensional array of air rod (n=1) on the squares and triangles lattice point.Utilize 15 2The grid of individual lattice point and 61 each band diagram of k vector sample calculation, the increment step-length of air coefficient of admission is 2.5%, the dense accumulation state until 90%.
With reference to Fig. 1-4, detect three groups of orientations (branch) band gap of TE polarization state.Maximum band gap is between low-frequency band, and its width almost increases linearly with the increase of air coefficient of admission, begins that of quick-make until it.To call it in the following text is main bandgap.On two directions of propagation, the main band gap of dividing almost stretches along whole air coefficient of admission.Be under 63% the condition at optimum air coefficient of admission (a.f.f.), divide band gap at Γ-directions X broad, the breadth extreme that reaches bandgap center frequency (m.g.f.) is 60%, and on Γ-J direction, it is that the m.g.f. that 65% condition is issued to is 55% (Fig. 3) at best a.f.f..
Two groups of directed band gap overlapping areas are pointed out the frequency range of complete (non-directional) photon band gap.Because under two extreme coefficient of admission scopes, little displacement is arranged between the branch band gap, the coefficient of admission scope of non-directional band gap reduces slightly, the scope of main bandgap is stretched over 87% from 10%.Further analyze and point out, the non-directional main bandgap is that the m.g.f. breadth extreme that reaches is 55% under 65% the condition at a.f.f..
For the TM polarization state, a direction is always arranged, the branch band gap is opened between most of low-frequency band.Yet, under these conditions, divide band gap seldom overlapping.In most a.f.f. scope, big branch band gap is opened along Γ-directions X between frequency band 1-2.Very big main branch band gap is opened between frequency band 2-3.In addition, under very low a.f.f. (37%) condition, it is (55%) opened along Γ-directions X rather than Γ-J direction, and causing a.f.f. is 55% little complete band gap when above.This is that the breadth extreme of condition lower edge Γ-directions X of 78% is 33% at best a.f.f., and is that the breadth extreme of condition lower edge Γ-J direction of 85% is 22% (Fig. 4) at best a.f.f..
The a.f.f. curve map of two polarization states is superposeed mutually, and unpolarized relevant (definitely) band gap is pointed out by overlap-add region.Fig. 1 and 2 explanation, the triangle dot matrix of etching air pore has absolute band gap really in the silicon.In addition, along the band gap of Γ-directions X greater than along on Γ-J direction.
Fig. 1 and Fig. 2 (not shown) that superposes mutually, non-directional is pointed out in the overlapping region, the frequency location of unpolarized relevant photon band gap.In this structure, be 55% full band gap to take place when above at a.f.f..
We have determined the analog result of square dot matrix configuration.In the case, the main bandgap of two kinds of polarization states is stretched over most of scope of a.f.f..In addition, the branch band gap of two kinds of polarization states is maximum on Γ-directions X, sums up as following:
Divide band gap The TE polarization The TM polarization
% bandgap center frequency Air coefficient % bandgap center frequency Air coefficient
Γ-directions X: ????45% ????55% ????53% ????88%
Γ-J direction: ????15% ????60% ????12% ????70%
Also analyze on the squares and triangles dot matrix in the air two-dimensional array of independent silicon post (pillar) as the function of air coefficient of admission and polarization state.Utilize 15 2The grid of individual lattice point and 61 k vectors calculate each band diagram.
For airborne silicon rod structure, we find that band gap is maximum under little air coefficient of admission, and its width reduces with the increase of air coefficient of admission.Fig. 5 and Fig. 6 represent the analog result of triangle dot matrix configuration.Two branch band gap of TE polarization state are opened, and are stretched over most air coefficient of admission scope.On two directions of propagation, very little overlapping region is arranged in the main bandgap, it points out the non-directional band gap of a.f.f. in 22% to 80% scope.Yet this band gap is relatively little (being to be 10% under 55% the condition at best a.f.f.).
For the TM polarization state, three big non-directional bandgap regions are arranged.It is 2%-82% that these bandgap regions occur in the air coefficient of admission respectively, and 15%-82% is in the scope of 25%-70%.Maximum (master) band gap is opened between frequency band 1-2, is that its width reaches 48% under 12.5% the condition at best a.f.f..
On any one direction of propagation, in fact there is not the overlapping region between two polarization states, therefore, this structure does not have unpolarized relevant band gap.
We have determined the analog result of silicon rod square dot matrix in the air.For the TE polarization state, on both direction, little branch band gap is being opened between the frequency band 4-5 and between the frequency band 6-7.At this moment, the branch band gap is the wideest on Γ-J direction, is stretched over most a.f.f. scope.Main branch band gap is that the breadth extreme that condition lower edge Γ-J direction of 33% reaches m.g.f. is 15% at best a.f.f., and the branch band gap is comparatively little (<8%) on Γ-directions X.
For the TM polarization state, in most a.f.f. scope, three big branch band gap between the frequency band 3-4, and are opened between the frequency band 6-7 between frequency band 1-2.Be that the breadth extreme that reaches on Γ-directions X and Γ-J direction is respectively 51%m.g.f. and 53%m.g.f. under 16% the condition at best a.f.f..On the both direction of every kind of situation, big overlapping region is arranged between the band gap island, the non-directional band gap of pointing out a.f.f. is respectively at 3%-62%, in the scope of 19%-63% and 25%-65%.This structure is not supported the unpolarized relevant band gap of full non-directional.
We also analyze the photon character of the squares and triangles array of etching air pore in the germanium.The refractive index of germanium (n=4) therefore, can expect that germanium produces very big photon band gap much larger than the refractive index of silicon, and still, in fact the band gap of germanium is similar to the band gap of silicon.
The character of silicon that we are also more identical and germanium photonic crystal.This is to realize by the non-directional band gap that the triangle dot matrix of analyzing the air pore disposes.The most remarkable aspect of band structure (Fig. 7 and Fig. 8) is, and is a lot of although the specific inductive capacity of germanium increases under any polarization state and any air coefficient of admission, do not have what variation and the size of low band gaps and position are actual.
Under little air coefficient of admission, very little displacement is arranged, (the band gap total energy level of germanium is low slightly) between the bandgap region of two kinds of materials.Along with the air coefficient of admission increases to the dense accumulation state that approaches, two areas are focused at together.
In the senior sub-bandgap zone of two kinds of polarization states, the displacement between the bandgap region is more remarkable.Though these areas are not focused at the closure of band gap, such a case occurs, for the TM polarization state, the main effects of change in dielectric constant is the size and dimension that changes the high band gap zone.
In fact, frequency shifting means that the size of germanium junction structure produces the desired size of given centre wavelength band gap less than silicon slightly.
Best coefficient of admission (in the case, band gap has maximum width) is, the air coefficient of admission is 65% under the TE polarization state, and the air coefficient of admission is 84% under the TM polarization state.On these aspects, the band gap of germanium only is 6.5%, greater than 8.4% of silicon band gap.Under every other air coefficient of admission, the increase of band gap width is in the extreme little.
Though the specific inductive capacity of germanium is far longer than the specific inductive capacity of silicon, the increase of band gap width is in the extreme little.The major advantage of silicon and germanium comparison is, it is very suitable for the optical communication window of 1.5 μ m, and pure germanium only is suitable for being operated in the above PBG device of 2 μ m.
We estimate the square dot matrix of imbedding silicon rod (n=3.46) in the silicon dioxide (n=3.5).Specific inductive capacity reduce to make the complete obiteration of TE polarization band gap slightly.We also show the branch band gap diagram of TM polarization state.The performance of research specific inductive capacity main bandgap when great changes will take place.Utilize the span (2-16, the increment step-length is 1) of specific inductive capacity, imbed the coefficient of admission figure of the triangle dot matrix of air pore in the calculation medium piece.For speed-up computation reaches reasonable levels (moving) on P90, utilize 13 2The grid of individual reciprocal lattice point calculates.This situation is enough to provide the accurate position (<5%) of low-frequency band and show total trend and relation.
With reference to Fig. 9-14, for the triangle dot matrix of air pore, the width of main bandgap is to use the three-dimensional surface graphical representation, and the width of main bandgap is and air coefficient of admission and ε b(equal refractive index n square) is relevant.For the performance of band gap is described, rectilinear also draws.These straight lines are represented the performance of band gap under a variable.
The size of the main TE polarized photon band gap of Fig. 9-11 expression is as air coefficient of admission and specific inductive capacity (ε b) function.Be under 55% the condition, to work as ε at best a.f.f. bIncrease to 2.25 when above, main bandgap is almost opened immediately.This is a low especially value, and it points out to utilize refractive index to be low to moderate 1.5 material, can set up non-directional (complete) TE polarized photon band gap.
As can be seen from Figure 10, at ε bUnder all values, the band gap size has identical asymmetric parabolic shape with respect to the air coefficient of admission.The size of band gap is at very little ε bValue increases with the fastest speed down, and at this moment, band gap begins to open.Along with ε bIncrease and reduce lentamente.Work as ε bIncrease at 16 o'clock, best coefficient of admission displacement about 10% linearly from 2.
Figure 11 points out, at little air coefficient of admission and big ε bValue down, band gap is with extremely slow speed increment, but it and ε bBetween relation be approximately linear.
The performance of Figure 12-14 expression TM polarization main bandgap is as ε bFunction with the air coefficient of admission.Be under 75% the condition, to work as ε at the optimum air coefficient of admission bMinimum value when being about 6 (n=2.45), TM polarization state main bandgap at first begins to open.With the performance comparison of TE polarization band gap, work as ε bDuring increase, TM polarization band gap enlarges in the scope of air coefficient of admission.
As can be seen from Figure 13, at ε bAll values under, the band gap size has identical asymmetric parabolic shape with respect to the air coefficient of admission.As the situation of TE band gap, at little ε bUnder the value, the size of TM polarization band gap increases with the fastest speed, and best a.f.f. is at ε bTrial stretch internal linear ground increase by 8%.
Figure 14 points out, at little air coefficient of admission and big ε bValue down, main bandgap in the approximately linear mode with ε bAnd increase.
Another critical nature of photon band gap is that the variation of centre frequency is as ε bFunction.Under the TE polarization state, centre frequency is with ε bBe subjected to displacement, but very little at given air coefficient of admission bottom offset.Displacement is being very linear before the optimum air coefficient of admission, particularly at big ε bValue down.Under the TM polarization state, the displacement of bandgap center frequency is an approximately linear in bigger coefficient of admission scope.As the situation of TE polarization state, the displacement of centre frequency is with ε bVariation be approximately linear.
Based on the triangle dot matrix that utilizes any general semiconductor or optical material to make, one group of data of Fig. 9-14 can be used for foretelling the character of photonic crystal.
Simulation and experimental result explanation, the nominal two-dimensional periodic structure of limited thickness can have the band gap that stretches along three-dimensional.This band gap can be held open in big angular range, and for high dielectric constant materials, can open simultaneously under two polarization states.So, do not need to make real three-dimensional structure in many cases to utilize the three-dimensional nature of band gap.
First embodiment of the invention
Relate in the application of using photonic crystal many, it is desirable to obtain the absolute photon band gap of complete sum.Under the situation of this photonic band gap structure, wave propagation is forbidden on any direction of propagation and is independent of polarization state.This provides a kind of fabulous photonic band gap structure to some application, for example, suppresses spontaneous radiation and polarization independent devices.Periodically triangle and hexagonal-lattice structure can be supported the complete photon band gap along the two and three dimensions direction.Yet, shown in Fig. 9-14, utilize sexangle and triangle lattice structure, only in very high dielectric constant material, can obtain the absolute photon band gap of complete sum (CAPBG), for example, GaAs (ε=13.6).The band gap frequency range that this structure forms also is highly to depend on direction of wave travel, and therefore, this structure is not suitable for all application.In addition, need big air pore diameter (big air coefficient of admission), so that set up the littler absolute photon band gap of complete sum.We find, because light leaks from the top on surface, increase the loss that the air coefficient of admission can increase photonic crystal.
In order to alleviate these problems, set about seeking isotropy band gap (being independent of direction) and little air coefficient of admission in the advanced low-k materials.Use low-index material to be convenient to make novel optical device with the optical fiber network system highly compatible.This device can comprise polarization-insensitive, the wave-division multiplexer filter of orientation independent and multiplexer.We have designed a kind of new structure, at low relatively refraction materials (silicon nitride ε b=4.08) with relative low air coefficient of admission (β=0.28) condition under, this structure has non-directional, the absolute photon band gap of the complete sum of polarization-insensitive.
Can prove that the anisotropy of photon band gap is relevant with the symmetry of photonic crystal dot matrix.The photonic crystal energy band diagram that relatively has square dot matrix (quadruple symmetry) and triangle dot matrix (sixfold symmetry) can easily be verified this point.Should be noted that symmetry is high more, with square dot matrix structure contrast, triangle dot matrix photonic crystal has bigger isotropic photon band gap.
Along with the inferior increase of symmetry level in the photonic crystal, Brillouin zone (BZ) just becomes round.The highest symmetry level of finding in the nature crystal is inferior to be 6, yet, in quasicrystal, can obtain senior time symmetry.Can utilize manual method to make quasicrystal.Senior time symmetry has the likelihood trend that increases the formation degenerate state.Conversely, this can reduce total photon band gap width, because the energy state of coincidence is arranged in the photon band gap.Yet we find, because the height isotropic structure of photon band gap, even total, still can obtain the absolute photon band gap of bigger complete sum because degenerate state may make the photon band gap width of the certain wave direction of propagation reduce.
In the real space, quasicrystal does not have the periodic property identical with crystal and shows that short distance is unordered.We are surprised to find, and the unordered arrangement of atom produces the Bragg peak value in Fourier space.Yet any quasi-crystalline real space approximate value always has the long-range periodicity of some form.The combination of these character provides some characteristics (as seeing) of deriving from normal crystal property to quasicrystal structures and from some other features (as seeing) of unordered character in the real space reciprocal space.Therefore, the combination results of part randomness and long-range periodicity optical characteristics extraordinary.
Because the simple unordered difference of short distance just can not define Brillouin zone (BZ) between quasicrystal and the crystal.Yet, can be referred to as (the zone of puppet-JZ), (puppet) Jones zone to quasicrystal definition.Puppet-JZ is the zone in reciprocal space, and reciprocal space is to be surrounded by the vector perpendicular bisector that is connected to main Scattering of Vector from initial point.JZ and BZ have many similar features, and provide normal periodic crystal and the periodically comparison of some forms between the quasicrystal.Most importantly similarly be to be similar among the normal PC Bragg reflection along the BZ border along the Bragg wave vector experience of puppet-JZ.Even meticulousr details, for example, the finishing of translational symmetry among the BZ, also with puppet-JZ in compatibility.Yet under the situation of puppet-JZ, the absolute amplitude of Bragg peak value is ungratified in the translational symmetry process.
Quasicrystal is to comprise the largest random set of paving at random.In the decoration scheme of suitable conception, each this paving corresponding to a kind of atomic structure.Pave model at random and add that decorating forecast scheme configuration determines the physical model of quasicrystal atomic structure at random.
Quasicrystal has with normal lattice structure surprising similarity is arranged, and wherein quasicrystal keeps the long-range periodicity scattering of light, even the ordered orientation of this structure is not the cycle.This formation for photon band gap is essential.This provides a kind of change photonic crystal symmetric means, so that produce bigger isotropic Brillouin zone.
Pave definite 10 heavy symmetric quasicrystals based on Penrose.It is the quasicrystal of knowing form that Penrose paves, and it is to be made of the adjacent oblique rhombus that different angles are arranged.According to the present invention, though this layout provides a kind of better photonic band gap structure, yet there is such problem, this paving is not easy to reproduce in crystal, because it is not structure cell or is similar to structure cell (unit cell) that structure cell can utilize photoetching method to duplicate on plane of crystal.So, be difficult to make the crystal of paving based on Penrose.
Someone advises based on the photon quasicrystal with 12 heavy symmetric square at random-triangle tiled systems.This structure be with silicon nitride waveguides in integrated be compatible, and have in the electromagnetic spectrum optical characteristics of visible/near infrared region, wherein can utilize various lasing light emitters.
Utilize the random collection of square and equilateral triangle to produce the photon quasicrystal structures.At random-Stampfli expansion rule application in squares and triangles set to produce quasi-crystalline high symmetry matter.In order to make this structure show long-range 12 heavy symmetry, need several times Recursion Application at random-Stampfli expands regular.People such as M.Oxborrow provide produce that the largest random squares and triangles paves at random-the Stampfli regular complete data that expands, [Phys Rev B48 (No.10) 6966 (1993)].Dotted line among Figure 15 (a) represent to be used to expand female dodecagon structure cell of scheme.Solid line represents that the sub-dodecagonal of expanding the parent crystal born of the same parents paves.The squares and triangles set that resides in any female dodecagon can occupy two unique orientations.This can obtain by female dodecagon being done 30 degree rotations.Therefore, before using the expansion rule, utilize the selection between normal and the female dodecagon structure cell of rotation, on this structure, form degree of randomness.In expansion scheme process, the reduced ratio of female dodecagon size is Thereby, form a plurality of sub-dodecagons.This a little dodecagonal center be added to each square or vertex of a triangle among the parent crystal born of the same parents.Air pore in the photon quasicrystal is positioned at the summit of each squares and triangles.Distance between the adjacent air pore is determined by spacing a.The layout of air rod in the dielectric material that Figure 15 (b) expression is studied, and the xsect of Figure 15 (c) expression waveguiding structure.This structure comprises: contain the silicon base of silicon dioxide cushion and be formed on suprabasil silicon nitride epitaxial loayer.Another silicon dioxide covering is configured on the silicon nitride.Etching covering and silicon nitride layer are to form the air pore.
Forming process is as follows:
The standard silicon substrate is by thermal oxide; produce the silicon dioxide cushion of little refractive index (n=1.46) and thick 1.8 μ m; utilize the silicon nitride layer of low pressure chemical vapor deposition method (LPCVD) deposition high index of refraction (n=2.02) and thick 250nm; thereby formation waveguide core; and also utilize the LPVCD deposition of thin (75~180nm) silicon dioxide coverings form the mechanical protection of a kind of anti-cut and dust at last.
Introduce photonic crystal as follows in waveguiding structure.Utilization write direct electron beam and plasma etching make and form figure on the wafer, thereby produce the cylindrical pore that (in the case) is stretched over sandwich layer/cushion interface downwards.At last wafer is dissociated into each device that carries out optical tests.
Another scheme is the engraving method of describing among our the application WO98/53351.Another feasible method of making photonic crystal is an etching anode, and it can be used for making the silicon based photon crystal of photon band gap, and this photon band gap is near infrared spectrum district (1.2~1.7 μ m).Under the anode bias condition in weak hydrofluorite (HF) solution, form porous silicon by the etching silicon metal.
Therefore, as can be seen,, for example, be formed on the summit of cell configuration, just can in crystal, duplicate structure cell by the air pore because structure shown in Figure 15 has structure cell.In photoetching process, utilize electron beam to produce basic structure cell, and determine adjacent structure cell by rotational coordinates 30 degree.
The photon quasicrystal of research is to be that 300nm and diameter are 180nm air bar construction by spacing a, is the silicon nitride interlayer of thick 260nm in the silicon dioxide on every side, is used to retrain light at two dimensional surface.
Utilize two-dimentional FDTD method, calculate transfer rate curve along all directions of wave travel.The FDTD method is based on equation of the ecentre space step scheme, and adds the exponential damping absorbing boundary condition.The Maxwell equation of discrete form is used to describe the electromagnetic field in the medium.The enforcement of equation of the ecentre space step is to count error for the biography that reduces this structure inscattering ripple.Utilize structural 1000 * 1000 contact grids of 30 row, make the photonic band gap structure discretize.Space increments (Δ h) is arranged to λ/50 with respect to minimum wavelength λ=350nm.Time increment (Δ t) is fixed on the Δ h/50c with respect to Δ h, and wherein c is the light velocity in the vacuum.
Initial input field is to be made of the Gaussian wave group in the spatial domain.The sample point of photon quasicrystal output terminal is collected the function of the field distribution of required electric field or magnetic-field component as the sample time.Fast Fourier Transform (FFT) (FFT) algorithm application is in the data of collecting, to provide the quasi-crystalline transport property of photon.The transfer rate curve map normalizes to the control analog result of propagating Gaussian wave group in the medium.Collect 14000 data points at each sampling contact, provide enough resolution to FFT.
In order to calculate angle for non-perpendicular to the transfer rate of the plane of incidence, make the photon quasicrystal rotate to required angle around its center, subsequently the finite difference grid application in this structure.
Figure 16 is illustrated in normal incidence (Γ J) under the quasi-crystalline condition of photon, and theoretical prediction band gap size is as the function of air coefficient of admission (β).Photon quasicrystal model has constant spacing a=300nm.The DIELECTRIC CONSTANT of silicon nitride core medium b=4.08.Even should be noted that very little β value, band gap is opened in the photon quasicrystal.Under the situation of β=10%, calculating along the band gap-bandgap center ratio of the Γ J direction of propagation is 12.9%, and for the simple triangle dot matrix of identical coefficient of admission and same media material, calculating along the band gap-bandgap center ratio of the Γ J direction of propagation is 2.5%.Even simulation is only in Γ J direction, because the height isotropy of photon band gap, band gap still is held open on all directions of wave travel, and this situation with the triangle photon crystal structure is opposite.
Carry out the degree of isotropy of other simulation tests with outstanding photon band gap.We study the photon quasicrystal of spacing a=300nm and air coefficient of admission β=28%.Utilize the FDTD method to calculate the transmission spectrum of several different directions of propagation between Γ J and the Γ X.Fig. 4 represents TE polarization mode and the TM polarization mode transfer rate along Γ J direction.The maximum of observing between the different directions of wave travel is changed to 4%.For the sake of clarity, the direction that the most extreme photon band gap changes of only drawing.The overall width of complete photon band gap is between 0.247a/ λ and 0.302a/ λ.Band gap-bandgap center ratio (Δ ω/ω that the TE mould is propagated 0) be 27%, and band gap-bandgap center ratio that the TM mould is propagated is 20%.Yet, can see that the TM band gap is the centre in TE band gap territory.This cause in the complete photon band gap of two different polarization states 74.1% overlapping, and under the same air coefficient of admission, triangle and hexagonal-lattice structure do not have the absolute photon band gap of complete sum.Under long wavelength's restriction (normalized frequency ω a/2 π c is less than 0.15), transfer rate is stretched over 1.Under these wavelength, propagation wave can not decompose the fine structure that square-triangle is paved, and quasicrystal is regarded as the homogeneous material of little refractive index.
Figure 18 and 19 comparison 12 heavy assymetric crystals and air coefficient of admission are 32% triangle dot matrix.As can be seen, PQC (photon quasicrystal) also has PBG.In addition, it is overlapping fully on frequency to observe the PBG of TE mould and TM mould.PBG is to last till 0.380 from 0.316 along Γ J direction.The main PBG normalization width Delta ω/ω of TE mould 0=18.4%, and the normalization width Delta ω/ω of TE mould 0=14.3%.Calculating the overlapping of TE mould and TM mould is 78.1%.Therefore, PBG remains on all wave vector directions of propagation, and the periodically PC contrast of common triangle dot matrix with same air coefficient of admission and specific inductive capacity does not wherein observe the overlapping of complete PBG.
Compare with triangle and sexangle photonic crystal, be also noted that band gap occurs on the low frequency.In Figure 14, TE polarized light and TM polarized light are at bandgap center (ω 0) normalized frequency located is respectively 0.273 and 0.275.With normal lattice structure contrast, nearest adjacent lattice vector is no longer determined the Brillouin zone.Brillouin zone in the reciprocal space is to determine that by the female dodecagon of dotted line among Figure 15 (a) it connects the lattice vector in several cycles always.
Figure 20 to Figure 25 shows the near field transmission characteristic variations of TE mould in different angle of propagation.The outstanding PBG in shadow region is present in all angles.Puppet that can not be brief-JZ explanation, because quasi-crystalline symmetry, about 15 degree should be identical for the characteristic at center, for example, 12 degree are closely related with the transport property of 18 degree.Therefore, quasi-crystalline character is isotropic basically, and is identical in any direction in 1%.
Figure 26 and 27 is mirror field curve maps.Because localization can be seen the little resonance in the bandgap region in the coupling of PQC surface and FDTD output port evanscent field, transmit and clearly illustrate in the district of forbidden band and can alleviate this problem, as shown in figure 26 without any resonance-characteristic by investigating the far field.Shall also be noted that PBG is the center with identical bandgap center frequency (0.351a/ λ) always, thereby confirm the isotropy of PBG band edge, the normalized frequency of band gap-bandgap center is reduced to Δ ω/ω slightly 0≈ 14.0%.When analyzing the angular relationship of this structure, PQC only needs maximum rotation 30 degree, just can obtain complete characteristic.This is owing to quasi-crystalline high symmetry, that is, owing to spend the repetitive nature of (representing 12 heavy symmetry) this structure and puppet-JZ thereof every 30.Yet it also is suitable utilizing along the quasicrystal mirror symmetry matter of the height plane of symmetry that can not brief puppet-JZ, obtains maximum Bragg reflection in the case, therefore only needs to consider along Γ J and Γ directions X (departing from normal incidence 15 degree), as shown in figure 27.In addition, should be noted that along the absolute transmission power of Γ directions X to be not equal to 1 that this is N/R, because when considering along this direction of propagation, what add on Γ J direction is absorbing boundary condition, rather than periodic boundary condition.The enforcement of PML influences the ability of collecting the output sampling face of all incident powers that comprise in the initial Gaussian wave group in the FDTD method, and this is because before output port was effectively collected, scattered light was absorbed by these borders.The absolute width that increases PQC structure in the FD space can alleviate this problem.
Figure 27 comparison TE polarization state and TM polarization state are along the TM reflectance properties of Γ directions X.TE polarization and TM polarized reflectance overlapping pointed out the overlapping of complete PBG zone.In the case, select high reflectance, its objective is that reducing any around the absolute width of PBG obscures with outstanding bandgap region.
The TM polarization analog result of the identical rotation quasicrystal approximate value of Figure 28 to Figure 30 (transmission diagram curve) expression, illustrate two polarization states and all optical propagation directions next time and with the absolute PBG of complete sum (CAPBG) of secondary.
Spectral decomposition is carried out transfer rate and is measured along the light of different directions propagation by dot matrix.Complete photon band gap experimental results show that in the quasicrystal of frequency spectrum designation TE polarization shown in Figure 31 and TM polarization.This experiment utilize to focus on the white light continuous spectrum that 100fs pulse of 1 μ J produces, it from the thick sapphire of 1mm be tuned to the regenerative amplifier of 850nm.Utilize this high brightness ultra broadband lasing light emitter to be convenient to the high precision transfer rate that wavelength transmits from 450nm to 1100nm by waveguide is measured.The optical fiber spatial filter that uses achromatic optical element and careful design is for being coupled to collimation and the aiming character that provides fabulous in the slab guide.Consider the scattering loss that the air pore causes, the normalization of the frequency spectrum among Figure 31, general description reduces throughput under the short wavelength.
Figure 31 (a) and (b) represent height isotropy first photon band gap of TE mould and TM mould under the different incidence angles degree respectively.Under each polarization state, consider three different angles of light, 0 °, 6 ° and 12 °.Measurement is with respect to the angle that couples light to the photon quasicrystal structures of quasicrystal surface normal.Figure 31 (c) expression incident light is along the quasi-crystalline experiment transfer rate of the identical photon curve map of Γ J direction.Can clearly be seen that three sharp band gap are similar to the analog result of prediction.In addition, should be noted that the transfer rate curve map has very strong modulated structure, these curves are very different with the curve that periodically photonic crystal is relevant.This is unordered owing to set up irregular short distance in the fine structure of transfer rate curve.In addition, TE polarization and TM polarization have the band gap of the identical central of residing in point, 0.39a/ λ, and 0.45a/ λ and 0.52a/ λ cause the absolute photon band gap of bigger complete sum.Under extinction ratio all frequencies in band gap greater than 95%, normalization width Delta ω/ω 0Scope be from 10% to 15%.
This frequency spectrum shows the identical fine structure, particularly Yu Ce angle and polarization state relationship with frequency spectrum shown in Figure 29.Yet, some differences are arranged on the absolute position of band gap.Compare with theory, the position of photon band gap is displacement 0.45, and their width reduces 1/2.Utilize two dimension (2D) model to carry out FDTD and calculate, this model is ignored actual three-dimensional (3D) character of waveguide in the planar structure.2D component k in the face of wave vector //The relation of propagating wave vector k with three-dimensional in the waveguide is a nonlinear relationship, and it causes the frequency displacement of all band gap.For the normal photonic crystal with similar performance, this is consistent with the three-dimensional model that utilizes plane-wave method.
About the relation between PBG performance and the background media specific inductive capacity, even low-down refractive index, for example, glass (n=1.45) and air coefficient of admission f=30.0%, photon band gap is held open.(b) there is complete PBG in Figure 32 (a) with (c) being illustrated under the TE mould, and the scope of PBG is from 0.409a/ λ to 0.443a/ λ, causes band gap-bandgap center ratio Δ ω/ω 0=7.9%.The band gap performance is pointed out to exist in the zone of high reflectance, and the power that pure transmission and reflection can't illustrate can be illustrated by diffraction effect.For the TM polarization state in the glass, in the case, Figure 32 represents along the reflectance analysis of Γ J and Γ directions X.Select the position of reflectivity again for the ease of the identification band gap region.The complete PBG of TM mould is stretched over 0.431a/ λ from 0.416a/ λ, produces minimum but complete band gap-bandgap center ratio Δ ω/ω 0=3.1%.Even complete TM band gap is to stretch in a zonule, it still is positioned at the centre of TE band gap, thereby very valuable CAPBG is provided.
Complete band gap is as the function of coefficient of admission in Figure 32 (d) expression 12 heavy quasi-crystalline glass materials of symmetry (n=1.45).
Transfer rate is confirmed, is possible with improved greatly coupling efficiency integrated photon quasicrystal device and fibre system in fact.This is the foundation stone of the active and Passive Optical Components of various novelties.Owing in this low-refraction, have CAPBG, can design maximum coupling efficiency and the sharp wave of polarization-insensitive is led elbow and beam splitter.This provides a kind of solution for extensive integrated optical device, and its center core layer can be made by silicon dioxide or quartz.
The loss of face external diffraction is when previous main obstacles factor in the senior PC device.In the design of waveguide PC, comprise the low-refraction sandwich layer and can make the performance of PQC more as a kind of face inner structure that relates to little modular angle degree.The outer wave vector component of face reduce to help to eliminate radiation loss.Yet the mould that the weak effect of restraint in the sandwich layer provides distributes and is stretched over the buffer protection layer.This weak sandwich layer constraint may have a negative impact to the PBG performance, and may cause device that bigger loss is arranged.In order successfully to analyze this effect, require to be embedded in the true 3D simulation of PQC in the glass waveguide.
In many transmission spectrums (as shown in figure 20), the modulation spectrum signature appears at the wavelength place away from photon band gap, and this forms very big contrast with normal PC, and normal PC shows smooth spectrum structure at these wavelength zones.This frequency spectrum details is unordered relevant with short distance, causes the strong localization of photon in the quasicrystal specific region.
Time average FDTD method is used to study the localization of interior TE polarization mode of photon quasicrystal and TM polarization mode.Figure 33 illustrates the constraint of TE mould in the photon quasicrystal.The TE mould is with the right side incident of wavelength X=1100nm from this structure.This λ resides in the band gap of structure.In the case, the localization that can see light mainly is in high dielectric regime.
This represents that block PQC provides a good environment can for high Q microdischarge cavities mould or photon localization.This local state plays a part very important for the low threshold value active device of design high-level efficiency.
The current acceptable method that forms the photon localization in photonic crystal relates to introduces defective in normal PC structure.The character of related defects state is very insensitive for fabrication tolerance, and therefore, manufacturing and high yield are very difficult reliably.
PQC (photon quasicrystal) provides such block structure, and it shows this state naturally, and the advantage with easy manufacturing and repeatability.
In addition, the high coupling efficiency of defect state in the PQC is even also can clear view arrive in above the growing in the structure relatively of 30 row.This can directly compare with single defective among the periodicity PC, and this defective has weak coupling efficiency.
The line number order of pore plays an important role in the design of PQC, because it directly influences the extinction ratio of wavelength in the band gap.Figure 34 represents the influence of this design factor.It is to be tangible among the above PQC of 17 row that strong PBG acts on thickness.The structure that has less than 17 row pores shows more weak band gap, but still the environment of localization is provided for low light level.
Utilize quasi-crystalline research in the reciprocal lattice space, investigate quasi-crystalline diffraction property (Figure 35).Big parent crystal born of the same parents produce the dodecahedron Brillouin zone, and that follows that solid white line points out can not brief triangle Brillouin zone.Real point battle array vector stretching is outside the edge of Figure 35 (a), and it determines basic reciprocal lattice vector 2 π/a.12 bright Bragg spots of central authorities are confirmed photon quasi-crystalline 12 heavy symmetry among Figure 35 (b).Figure 35 (b) illustrates Edwald ball structure.Choose the reference point of central Bragg peak value as this structural scheme.The dot-and-dash line circle is a tectonic line.These lines point out to connect the equidistant path of any bright Bragg peak value and center reference point.For the sake of clarity, the do not draw tectonic line of more weak Bragg peak value.These lines are represented reciprocal lattice vector k GThe real camber line of grey is represented the Edwald spherical segment of wavelength X=633nm, its reciprocal vector k In=2 π n Eff/ λ.Should be noted that for consistent with experimental result better, use effective refractive index n Eff=1.98, rather than the absolute index of refraction n of silicon nitride material.Suppose that all k vectors have identical n EffBecause highly isotropic Brillouin zone can be verified this approximate.The grey circle determines that wavelength is the projectional angle of the far field construction distribution of 633nm, k with the joining of tectonic line Diff=k In+ k GThese are pointed out by solid white line.In theory, expect that this quasicrystal is diffracted into 12 light beams to incident light.Yet, actually, be invisible from the diffraction light of weak intensity Bragg peak value.
Make the photon quasicrystal of various parameters, it shows good repeatability and stability.The electron scanning micrograph of Figure 36 (a) expression typical device, recording its spacing is that 300nm and coefficient of admission are 28%.The photo that the little photon quasicrystal of Figure 36 (b) expression is in operation.The photon band gap along continuous straight runs resides in the top of photo.The horizontal edge of below is corresponding to the waveguide surface of cleavage.The TE polarized light of 633nm focuses in the cleavage waveguide from the bottom of photo, then, impinges perpendicularly on photonic band gap structure again.It shows quasi-crystalline experiment far field construction.
The angle of the expection of Edwald spherical structure shown in the angle of diffracted beam and Figure 36 (b) is directly compared.
Table 1
The experiment light beam The angle of figure A7 Theoretical light beam The angle of figure A2a
????A,A′ ????B,B′ ????C,C″ ????D ??20.9,18.8 ??36.3,33.0 ??51.3,50.1 ??66.3 ????1 ????2 ????3 ????4 ????18.0 ????34.6 ????51.3 ????67.9
Table 1 is listed the experiment and the point of theory of the photon quasicrystal diffraction of 633nm radiation.
The theoretical angle of diffraction of table 1 explanation is very consistent with the experiment angle of diffraction.This consistent successful manufacturing and the diffraction property that photon quasi-crystalline 12 heavy symmetry is described and confirms it.
Second embodiment of the invention
With reference to Figure 37, this is a device of representing to have normal triangle photonic crystal dot matrix with graphic form, and it shows photon band gap in the presetted wavelength scope.
This dot matrix is divided into two zones, zone 1 and zone 2.There is the sub-dot matrix that comprises one group of defective bit in each zone in these two zones, and these defective bit are to be made of one group of pore (12,22) in per the 4th position, and these pores have smaller diameter (or bigger pore diameter is arranged) than pore in the block dot matrix.In the wavelength coverage of photon band gap, they have the effect of introducing narrow defective mould.The wavelength of this defective mould depends on flaw size consumingly.
In the first area size of defective 12 be different from (greater than) size of defective 22 in the second area, though the flaw size in each zone is identical.Each defective is set up microdischarge cavities, and it can support the local mode of wavelength in the photon band gap.Though the defective mould is confined to the position of defective, it has relative evanscent field function (Figure 38), can penetrate several rows and enter dot matrix (being similar to quantum tunneling effect) on every side.If a plurality of identical defective bit are incorporated in the normal dot matrix, therefore, the evanscent field relevant with the constraint mould overlaps each other, and then microdischarge cavities becomes optically-coupled, and photon can be crossed over block dot matrix from a defective bit and transfer to next defective bit.On the wavelength in photon band gap, transmission can be crossed over photonic crystal.The wavelength of this defective mould and the size of defective have very large relation.On the other hand, overlapping as if not having between the evanscent field relevant with adjacent defective bit, then in the photon band gap wavelength coverage, there is not the transmission flaws mould.
Defective can be arranged on the regular figure in the photon band gap dot matrix, or is arranged at random or the quasirandom mode formula.The efficient (and speed) of transmission depends on the coupling efficiency between the microdischarge cavities.
In the energy range of photon band gap, two groups of defectives are introduced the transmission flaws mould effectively.Yet because the defective wavelength is different in the both sides of knot, for example, the energy level of defective mould is in the zone 2 lower (Figure 39) on right side.
For photon can from left to right be propagated by this structure, these photons must lose some energy (Figure 39).This is equivalent to wavelength or change in color.Similarly, photon can not be propagated along opposite direction, because this just relates to a small amount of increase (Figure 39) of energy.
So far we think always, and photon can spontaneously not change its wavelength in passive material, therefore do not have loss mechanism.Yet we find, the material with lattice structure of the present invention, and for example, above-mentioned silicon nitride structure (or silicon oxynitride structure) is showed non-linear (power is relevant) wavelength shift effect.The relevant wavelength shift effect of this power is impelled the operation of above-mentioned diode junction device.Therefore, by sending the left field (1) of high power signals,, can reduce the wavelength (in zone 1) of defective mould, allow high power signals to cross over this knot and propagate into the right side area (2) of device because this structure is non-linear to device.
Yet if send (from zone 2 to zone 1) along opposite direction, the non-linear defective mould wavelength that makes of material further reduces, just do not have be tuned to the suitable defective mould of zone (1) medium wavelength, therefore, transmission can not be carried out.
Setting up non-linear required optical power threshold level is similar to and must be added to semiconductor pn and ties to obtain the bias voltage that electricity is led.
Another kind of operation method is based on the photonic crystal (Figure 40) of two zoness of different.Each zone is to be made of flawless normal triangle dot matrix photonic crystal.Yet each zone design becomes to have different slightly photon band gap wavelength coverages.(this can obtain by changing lattice distance and/or pore diameter).
By adding the side of high power light pulse to knot, the edge of band gap produces displacement.Such situation can take place, and wherein band edge produces displacement, opposite regional band edge coincidence in the wavelength of these band edges and the device.At this moment, transmission can be carried out, thereby produces diode action.
Utilize high-power second laser beam to add optical biasing to device, can make photoswitch, wherein a small amount of excess power of providing of signal beams can make the band gap coincident.The band gap coincident is not important.Importantly, before adding excess power, signal wavelength should be positioned at a photon band gap, rather than in another photon band gap, when adding excess power, signal wavelength should break away from this two photon band gaps.
With reference to Figure 41 to Figure 45, various other the embodiment of they expression the present invention.Figure 41 is based on the diode structure of crystal lattice structure shown in Figure 40, and wherein the high power input beam from the left side provides an output beam, and is blocked from the high power input beam on right side.This is because two photon band gaps that two zones 30,32 of crystal lattice structure provide have different slightly coboundary values.When the high power input beam when the left side is imported, the non-linear energy that makes the band gap coboundary of lattice structure 30 is to bottom offset, therefore, the wavelength of input beam is on top on the edge.So the emission of light is on two coboundarys, thereby provide an output beam.Yet, from the influence of light lattice structure 32 on right side, the coboundary of photon band gap is reduced, still, the photon band gap in the zone 30 still remains unchanged.Therefore light is blocked.
With reference to Figure 42, this figure has and is similar to structure shown in Figure 44, but wherein provide the high power bias lighting signal 34 of any required wavelength, its photon band gap is reduced, thereby input low-power signal 36 transmission that allow signal wavelength are by this structure, so that an output beam 38 to be provided.This structure provides relaying or switching function.
With reference to Figure 43, it represents the concrete form among Figure 42 embodiment, and wherein low-power signal 36 and high power offset signal 34 are transferred to structure 30,32 through fiber path 40,42.
With reference to Figure 44, the synoptic diagram of the transistor arrangement of structure 30,32 among Figure 41 is adopted in its expression.High power biasing light beam 50 is added on the zone 30, is used for the photon band gap of modulation areas 30, thereby allows part input beam 36 to launch as output beam 38.Therefore, by regulating the parameter of power and signal wavelength meticulously, the effect of power optical beam 50 is the power of modulation output beam 38, and its working method is similar to transistor.
In Figure 45, the lattice structure 52 of employing comprises the signaling zone of normal triangle dot matrix.Be added to the lip-deep high power signals light beam 54 of crystal structure and change photon band gap, allow light to propagate and pass through crystal structure as light beam 56.
We are from experimentally having determined to have the precise characteristics that is similar to the crystal structure of regional 1 form Figure 40, shown in Figure 46 and 47.Figure 46 represents TE mould and the propagation of TM mould outside band gap, that is, its energy is greater than the energy of energy level on the band gap, but is in close proximity to band edge, and Figure 47 represents the propagation of these two patterns at band gap coboundary energy level place.
In Figure 46, the illustration of lower left is represented the relation between signal wavelength and the band gap, and signal wavelength surpasses 700nm, and band gap is the zone at about 600nm.Master map is the frequency spectrum of the frequency spectrum of comparison signal laser beam signal on two different power levels (photon crystal structure of having imbedded in having transmitted by silicon nitride waveguides) and reference laser beam (transmitted by similar waveguiding structure, but the photonic crystal of wherein not imbedding) among Figure 46.
As can be seen, approach two patterns of band edge for wavelength, when power when low-power (shown in the curve of bottom) changes over high power (shown in the curve of top), what variation is the frequency spectrum character of reference laser beam do not have.
Yet, when power when low-power changes over high power, the signal beams spectral shape that transmission is passed through changes a lot, this signal beams has transmitted and has passed through photonic crystal.
Compare with reference signal, the spectral shape of laser beam becomes smooth, and is displaced on the longer wavelength slightly.
This effect is to strengthen owing to the localization that approaches band edge makes optical power density.The optical power density that strengthens is send out non-linear of predisposition and the effective refractive index of silicon nitride material is changed slightly again.This situation makes the band gap edge dislocation to suitable position again.
Referring now to Figure 47, these curve representation photon crystal devices are the relevant performance of the power on the short wavelength in photon band gap.The relation of expression signal wavelength and band gap in the illustration of upper left side, wavelength value is near 610nm.
As can be seen, for the TE mould, transmission is roughly the same with reference spectrum under high power and low-power by the spectrum light beam of photonic crystal, though the frequency spectrum of signal beams has little displacement to long wavelength side.
For the TM mould, under low-power and high power, very big difference is arranged between the signal spectrum of reference spectrum and emission.
In both cases, big displacement has taken place to long wavelength side in the signal by the photonic crystal emission.Under low-power (shown in the side accompanying drawing of lower-left), the peak value center that transmits is about 620nm.For the high power input signal, the spectrum of wavelengths center that transmits is about 627nm.Therefore, under the influence of photon band gap, brought out the relevant wavelength variations of power to signal.
This causes owing to high-power photon band gap edge is subjected to displacement, and is displaced to high slightly wavelength (lower energy).This edge dislocation is because the non-linear of lattice structure causes.Should be noted that silicon nitride material itself is not a nonlinear material, and the triangle lattice structure is brought out the nonlinear effect of very strong linearity.In this technical specification, the nonlinear meaning is that the refractive index of material depends on added optical signal power.

Claims (38)

1. method that forms the structure of showing photon band gap, this method comprises:
A kind of material that stretches along two-dimensional directional is provided, and in described material, be formed with the first area of first refractive index, the first area is separated by the second area of second refractive index or a plurality of second area, long-range order and the unordered quasicrystal of short-term are determined to show in these zones, and show that n weighs symmetry, wherein n is more than or equal to 2, thereby a photon band gap that stretches along described two-dimensional directional at least is provided.
2. structure of showing photon band gap,
Wherein this structure comprises the material that stretches along two-dimensional directional, this material comprises: the first area of first refractive index, the first area is separated by the second area of second refractive index or a plurality of second area, in order that a kind of long-range order and unordered quasicrystal of short-term showed is provided, and show that n weighs symmetry, wherein n is more than or equal to 2, thereby sets up a photon band gap that stretches along described two-dimensional directional at least.
3. method that forms the structure of showing photon band gap, this method comprises:
A kind of material that stretches and have relative low-refraction along two-dimensional directional is provided, refractive index is less than or equal to 3, with the first area that in described layer, is formed with first refractive index, the first area is separated by the second area of second refractive index or a plurality of second area, long-range order and the unordered quasicrystal of short-term are determined to show in these zones, and show the heavy symmetry of n, wherein n is more than or equal to 2, thereby sets up a photon band gap that stretches along described two-dimensional directional at least.
4. one kind forms the method for showing photonic band gap structure, and this method comprises:
A kind of material that stretches along two-dimensional directional is provided, and in described material, be formed with the first area of first refractive index, the first area is separated by the second area of second refractive index or a plurality of second area, long-range order and the unordered quasicrystal of short-term are determined to show in these zones, and show that n weighs symmetry, n 〉=12 wherein, thus a photon band gap that stretches along described two-dimensional directional at least set up.
5. method that forms the structure of showing photon band gap, this method comprises:
A kind of material that stretches along two-dimensional directional is provided, and this material of etching is to remove the material in the predetermined area, etching is to stretch along the direction perpendicular to described two-dimensional directional, thereby define the first area of first refractive index, the first area is separated by the second area of second refractive index or a plurality of second area, thereby determine to show long-range order and the unordered quasicrystal of short-term, and show that n weighs symmetry, wherein n is more than or equal to 2, thereby set up a photon band gap that stretches along described two-dimensional directional at least and
Wherein the ratio of first area area and second area area is relatively low, and it is less than 35%.
6. according to any method or structure in the claim 1 to 5, be roughly uniform on any direction of photon band gap in described two-dimensional directional wherein, photon band gap has identical width and/or identical bandgap center frequency.
7. according to the method or the structure of claim 6, wherein photon band gap along the homogeneity of any direction in 4%, preferably in 1%.
8. according to any method or structure in the claim 1 to 7, wherein photon band gap is roughly the same in all polarization states.
9. according to the method for claim 5, wherein this ratio is less than or equal to 28%.
10. according to the method for claim 5 or 9, wherein said predetermined area comprises described first area.
11. according to the method for claim 10, wherein said first area comprises the air pore.
12., wherein be full of material requested subsequently in the air pore according to the method for claim 8.
13. according to the method for claim 12, wherein material requested is a liquid crystal, ferromagnet, and dyestuff, or optical nonlinear material, its optical property may be subjected to applied field, magnetic field, electromagnetic field, or light field, temperature, sound radiation, or the influence of chemical reagent.
14. according to any structure or method in the above claim, wherein quasicrystal is showed 12 heavy symmetry.
15. according to any structure or method in the above claim, wherein quasicrystal has cell configuration.
16. according to the structure or the method for claim 14 or 15, wherein approximate value is paved and is based on adjacent rectangle, the set of triangle or rhombus.
17. according to any structure or method in the claim 1 to 13, wherein quasicrystal is showed 10 heavy symmetry, it is based on Penrose and paves, or quasicrystal is based on Archimedes and paves.
18. according to any structure or method in the above claim, wherein this material is selected from silicon, germanium, silicon nitride, silicon oxynitride, arsenic potassium or indium phosphide, or their compound or potpourri, or glass, or plastics.
19. according to the structure or the method for claim 18, wherein this material is silicon nitride or silicon oxynitride.
20. according to the structure or the method for claim 18, wherein this material is a glass, preferably quartz glass.
21. according to any structure or method in the above claim, wherein said first area is positioned at the summit of crystal lattice, or is positioned at the center of shaped position.
22. according to any structure or method in the above claim, the quasicrystal geometric shape along two-dimensional directional is determined in wherein said first area, and n>6.
23. according to any structure or method in the above claim, wherein said material stretches along three-dimensional, and stretch along the direction perpendicular to described two-dimensional directional described first area.
24. according to the structure or the method for claim 23, wherein this material comprises optical fiber, and described first area is along the direction stretching, extension of fiber lengths.
25. according to any structure or method in the claim 1 to 21, wherein the first area forms along the length parallel to each other of a direction in the two-dimensional directional, this length is such along the second dimension direction at interval, in order that the described photon band gap along described at least two-dimensional directional is provided, and wherein n more than or equal to 2.
26. a structure of showing photon band gap,
Wherein this structure comprises the first area material that contains first refractive index, the first area is separated by the second area of second refractive index or a plurality of second area, in order that a kind of crystal or quasicrystal of showing photon band gap is provided, thereby the character that changes material to be to bring out significant nonlinear effect, and wherein the refractive index of this structure depends on and incides this structural luminous power.
27. optical device, comprise: the entity that has a paths at least, the optical radiation transmission is by this path, wherein the time across described path, the transport property of described radiation is subjected to the constraint of interior first area of described entity and second area, and comprise: a kind of material or the multiple material of showing photon band gap, position between wherein said first area and second area are mutual is such, the relevant evanscent field of the described first area photon band gap evanscent field relevant with described second area photon band gap interacted, thereby making described transport property is non-linear basically, asymmetric or controlled.
28. optical device, light transmission path by the first and second adjacent areas is arranged, each area comprises: the first area of first refractive index, the first area is separated by the second area of second refractive index or a plurality of second area, described zone defines the crystal or the quasicrystal structures of photon band gap, each this structure is defectiveness therein, thereby set up photon state and relevant evanscent field in the band gap, the evanscent field of first area and second area is coupled mutually, thereby allow to transmit in photon band gap, transport property is non-linear or asymmetrical.
29. device according to claim 28, wherein the defect sturcture of each area is to be formed by predetermined first area, there is size or the shape that is different from other first areas this first area, or this first area is that different materials forms, or omit predetermined first area formation, thereby set up one group of defective of coupling mutually by evanscent field.
30. according to the device of claim 29, wherein defect sturcture comprises: the periodicity defect array.
31. according to the device of claim 29 or 30, wherein the defective in first area is the defective that is different from the second area, and/or the interval that is different from defective in the second area is arranged.
32. optical device, light transmission path by the first and second adjacent areas is arranged, each area is to be formed by such material layer, this material comprises: the first area of first refractive index, the first area is separated by the second area of second refractive index or a plurality of second area, these zones define the crystal or the quasicrystal structures of photon band gap, and the photon band gap in two areas has different values, incides the band gap magnitude of a light adjustment on the area with respect to other area band gap thereby make.
33. according to the optical device of claim 32, wherein at least one area is showed nonlinear refractive index in first area and the second area.
34. according to the optical device of claim 32 or 33, wherein band gap is adjustable, thereby its band gap magnitude is equated.
35. according to the optical device of claim 32,33 or 34, wherein first area is different with crystal or quasicrystal structures in the second area separately, has different symmetry, and/or there is different size and/or at interval the first area separately.
36. photoswitch that comprises according to the structure in the claim 26, comprise: the conduct power light beam is to this structural device, and comprise: the pilot signal light beam passes through the device of this structure, thereby makes power optical beam change the refractive index and the path of setting up a bars light beam of material.
37. an optical diode that comprises according to any optical device in the claim 27 to 35 comprises: the pilot signal light beam is by the device of transmission path.
A 38. photoswitch or transistor that comprises according to any optical device in the claim 27 to 35, comprise: the pilot signal light beam is by the device of transmission path, with the device of guiding modulated beam of light to first area and/or second area, be used to change its refractive index, thereby change the transport property of transmission path.
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GB0008546D0 (en) 2000-05-24
CA2404743A1 (en) 2001-10-18

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